In the U.S. Pat. No. 2,936,847 issued on May 17, 1960, there is disclosed a mobile lifting equipment with an extensible boom structure which includes controls which will prevent movement of the boom structure into zones or sectors which would cause the vehicle to tip over. These controls which are provided serve to prevent downward movement of the boom structure below a certain angle when the boom structure is in certain danger sectors or zones until the outer end of the boom is retracted a predetermined distance. Such control systems have the disadvantage in the event that they become operative to prevent the lowering of the boom, some means must be provided for overriding the controls so that the boom can be retracted and brought back to the ground. Such control systems also have the disadvantage in that they are relatively complicated. There is therefore need for a new and improved lifting equipment having a telescoping boom with automatic extension limiting which overcomes such disadvantages.